what is water?
A precious resource
We need fresh water to drink, to wash our hands, to cook, and to water plants, amongst other things. Without water, plants would die and people and animals would go thirsty.
There is a fixed amount of water on Earth, but only about 3% of it is fresh and available for drinking by humans, plants and animals. The other 97% of water, which is mostly stored in the world’s seas and oceans, is salty and undrinkable.
Because there is a limited amount of fresh water on Earth, it is very important that humans use water wisely.
Water - solid, liquid and gas
A water molecule is made up of 2 hydrogen atoms and 1 oxygen atom (H20). Pure water is tasteless, odourless, and nearly colourless.
In the water cycle, water can exist in 3 different states – solid (snow, ice), liquid (rainwater, saltwater), and gas (water vapour).
| Solid | Liquid | Gas |
|---|---|---|
|
Ice, snow, and frost are examples of water in its solid state. Liquid water freezes at 0oC (Celsius). Celsius is a scale that measures temperature. Other examples of solid water are ice cubes, icicles, hail and sleet. |
Liquid water is found in many places - in the oceans, rivers and creeks. Liquid water is what falls from the sky when it rains, and what comes out of your tap. |
Water in its liquid state may evaporate - to change into water in its gaseous state. Water evaporates with the help of heat. Changes in temperature can increase the rate or how long it takes water to evaporate. Water can evaporate from soil; from wet clothes hanging on a clothesline; from plants; and when we breathe out. |
How do we measure quantities of water?
| Unit | Abbreviation | Definition |
|---|---|---|
| Millilitre | ml | Fills 1 cubic centimetre, cm3 |
| Litre | l | 1,000 ml |
| Kilolitre | kl | 1,000 litres (fills a cubic metre, m3) |
| Megalitre | ML | 1,000,000 litres |
| Gigalitre | GL | 1,000,000,000 litres |